This invention relates to methods and apparatus for forming fabric tubes, and more particularly relates to methods and apparatus for rapidly and accurately manufacturing tubular filter bags from a web of material.
Numerous air filtration systems include therein filter bags of felt or woven fabric material which function to remove solids from the air passing therethrough. Such bags take the form of tubes usually open at both ends may be of the outside-in or inside-out type depending upon the direction of flow of the influent solid-laden air therethrough. Thus, in the outside-in type of bag, the influent flows from outside the bag where solids are retained and the clean effluent air is removed from within the bags. The direction is reversed in the inside-out type of bag and solid laden influent is fed to the inside of the bag and the solids in the air are retained inside the bag. In this type, the clean effluent air is removed from the region exterior to the bag.
Such filter bags have met with great success in systems for industrial purification of air, as well as in commercial operations. In any event, in these systems, it is common to employ the bags in a unit that may contain twenty to thirty of the bags operating in parallel and connected to a common manifold.
The diameter and length of each bag, whether used singly or in combination with other bags in a manifold system, varies depending upon the particular use to which the bag is to be put and the requirements of the system into which its installation is contemplated.
In any event, it has been the practice in the past, to form such bags by hand methods and with the expenditure of substantial amounts of manual labor. Thus, it has not been uncommon to precut material into sheets by hand using common scissors. These precut sheets have then been hand manipulated to overlap the edges as the material is manually fed into a sewing machine for a tube with a seam along one side.
Filter bags today are formed from various materials such as natural and man made fibers, as well as felt. Natural fibers in general can be readily handled by operators sewing filter bags. However, fiberglass in particular, and certain weaves of polyester and acrylic are not only difficult to handle, but are somewhat abrasive and are found to injure the hands of the operators. Correspondingly, while such hand methods have in the past been used in the manufacture of filter bags of various synthetic materials, such methods have suffered from the disadvantage that those required to handle and manipulate certain synthetic materials, for example, fiberglass, are injured as a result of the nature of the material. Thus, it was not uncommon at the end of a work day for the hands of the operators to be swollen and bloody from abrasions and the numerous pricks received in handling the glass fiber sheets.
These disadvantages of the prior art are overcome with the present invention and commercially acceptable embodiments of a fabric tube former and the like are herein provided which are not only fully capable of fashioning filter bags under most operating conditions but which are also fully capable of other tasks completely beyond the capabilities of the methods and devices of the prior art. More particularly, however, the embodiments of the present invention are capable of operation with a much higher efficiency and accuracy and at a substantially reduced operating cost.